Communication satellites have become commonplace for use in many types of communication services, e.g., data transfer, voice communications, television spot beam coverage, and other data transfer applications. As such, “bent pipe” satellites transmit and receive large amounts of signals that may use a “multiple spot beam” configuration to transmit signals to desired geographic locations on the earth. Mobile applications such as telephones and personal digital applications are also becoming increasingly popular.
Architectures having the ability to track the position or location of a mobile user are now known. These systems allow for a decrease in platform stability requirements, which in turn can lower the overall cost of the system. One exemplary architecture is disclosed in application Ser. No. 09/587,758 and provides for a third generation (3G) mobile communications system to mobile terminals. The 3G mobile communications system provides high data rate communications to a user enabling simultaneous voice, data and entertainment communication. Knowledge of user location allows for fewer code division multiple access (CDMA) code handoffs. In a fixed-cell-structured system, when a user crosses a boundary of two cells, CDMA code handoff must happen to avoid interference. With a beam following a user scheme, the user would not have to change his CDMA code unless he gets too close to another user who is using the same CDMA code. This system uses a global positioning system GPS to determine the position of a user and thus the user terminals need to be GPS enabled so as to decrease handoffs and avoid interference. However, global positioning systems can be costly to produce due to the inclusion of hardware into the mobile user terminals.
The architecture of the above system allows the mobile terminals to communicate with the gateway through multiple stratospheric platforms. Each platform has array elements that are transponded to and from the gateways where beamforming is performed digitally rather than implementing a complete phased array antenna on each of the platforms. This array configuration allows the gateway to form beams for each individual mobile terminal and track the moving terminals. Multiple platforms in a region increases system capacity by allowing frequency reuse with the directional mobile terminal antenna or by providing additional processing gain for a given terminal.
Additionally, various methods for location tracking of mobile users are also known. These methods allow the systems to track mobile terminals within the system. One such location tracking system is based on a two-way ranging method. One implementation of this method is through polystatic triangulation which utilizes three platforms where forward signal paths can be different from the return paths. The system can be calibrated by providing triangulation to earth stations. Other methods of tracking mobile users are also well known.
While the above-described methods and systems are satisfactory, a continuous concern of mobile communication engineers is to increase performance and reduce the number of components used in a mobile communication system. Reducing the number of components is important because it decreases weight, decreases costs involved in production and implementation, and potentially increases accuracy and efficiency of the communication system.
It would therefore be desirable to develop a mobile communication system with fewer components and increased efficiency and accuracy that also allows for the communication of data, voice, and other information to the mobile terminal.